1. Field of the Invention
The present invention relates to a color filter for a liquid crystal display, a process for producing the liquid crystal display, and a liquid crystal display device employing the color filter.
2. Related Background Art
Generally, liquid crystal display devices are employed for various uses such as personal computers, word processors, automobile navigation systems, and miniature television. The demand therefor is increasing in recent years. Correspondingly, reduction of the production cost thereof is strongly desired.
The color filter for the liquid crystal display device is constituted of arrangement of an number of picture elements comprising respectively color segmental layers of red (R), green (G), or blue (B), and light-intercepting black matrixes in the peripheries of the color segmental layers to increase the display contrast. The respective color segmental layers of the color filters comprises a coloring material which selectively transmits R, G, or B. The coloring material includes dyes and pigments. Pigments are widely used since the pigments are more durable.
The colored picture element portions of the color filter are formed by dying, pigment dispersion, pigment electrodeposition, or a like method.
To meet the demand for the cost reduction of the color filter, printing methods and ink-jet methods are proposed for formation of the colored picture element portions. The printing methods, however, involve steps of transfer of a coloring matter from a printing plate and drying of the printed matter for each of the colors of R, G, and B repeatedly, namely three times. The production efficiency of printing methods is disadvantageously poor.
In the ink-jet methods, on the other hand, three coloring liquids containing a coloring matter of R, G, or B are ejected on a substrate by an ink-jet method, and the deposited coloring inks are dried to form colored picture element portions, as shown, for instance, in Japanese Patent Application Laid-Open No. 59-75205. The ink-jet method enables simultaneous formation of picture elements of R, G, and B, thereby simplifying the production process greatly and reducing the production cost remarkably.
In formation of color layers with ink dots by ink-jet method, color mixing is liable to occur at the boundaries between different colors of color segmental layers. In particular this phenomenon is remarkable when the gaps between the color segmental layers are narrowed. The color mixing between the different colors of the color segmental layers impairs the image quality of the liquid crystal panel, and lowers the yield of the filter to raise the production cost. Therefore, the ink-jet method requires broad gaps between the segmental color layers such that the color mixing is not caused. This makes it difficult to increase the number of picture elements in a certain area to raise the fineness of the image.
The use of a pigment improves the heat resistance and the lightfastness of the filter. However, the pigment dissolves the light polarization effect owing to its light scattering more remarkable than dyes to lower the image contrast of the liquid crystal panel.